A collapsible tank is a type of storage container that can be relatively easily and quickly transported and deployed. Typically, a collapsible tank is made of a foldable material, such as a fabric, that can be folded during transport and unfolded for installation. Collapsible tanks are commonly used to store liquid products, such as fuel or water, in remote or temporary locations where a more permanent rigid storage tank is impractical. For example, collapsible tanks can be used to temporarily store fuel at a tactical location for military operations.
Tracking inventory of a product stored in a collapsible tank presents problems that are not encountered when storing a product in a rigid storage tank. To determine the volume of a product stored in a rigid tank, one could employ a level detector, such as a radar level detector or an ultrasonic level detector, to determine the current level of product in the rigid tank. The volume can then be calculated using the current level and the known dimensions of the tank. Another conventional method for determining the volume in a rigid tank involves the use of a pressure gauge installed at the bottom of the rigid storage tank. One could take a pressure reading and calculate the volume of product in the rigid tank using the dimensions of the tank and the density of the product stored in the tank. However, these methods for determining volume of product stored in a rigid tank can not be used to accurately determine the volume stored in a collapsible tank. As a collapsible tank is filled with a product, the shape of the collapsible tank changes as the sides of the collapsible tank bulge out and the top is elevated. Also, the collapsible tank can conform to the terrain of an installation environment that may not be flat or level. Thus, the dimensions of the collapsible tank can vary causing inaccurate calculations using the above described methods for determining the volume in a rigid storage tank.
One conventional method for determining the volume of product stored in a collapsible tank involves a person stretching a string across the top of the tank such that the string is parallel to the ground and just touching the top of the tank. The person then measures the height of the string from the ground. Finally, the person looks up the level of the tank corresponding to this height in a book containing tables of level to volume correlations generated by the manufacturer of the tank. This method suffers from inaccuracies due to unlevel ground and imperfections in the tank dimensions and materials (e.g., bulges in the material). This method can also suffer from human error. For example, the person may not hold the string level and parallel with the ground or may incorrectly and imprecisely measure the height of the string. Additionally, this method is time consuming and an expensive use of man-power.
Another conventional method for determining the volume of product stored in a collapsible tank involves metering all product into and out of a collapsible tank and then calculating a volume based on these movements. For example, if the tank is empty and 20,000 liters is pumped into the tank according to a flow meter, then the calculated volume is 20,000 liters. If 5,000 liters is subsequently pumped out of the tank according to a flow meter, then the new calculated volume would be 15,000 liters. This method often leads to problems as an operator may forget to use a meter for every movement or forget to reset the meter before moving product. Additionally, the flow meter can sometimes malfunction during a product movement resulting in an inaccurate measurement for that product movement.
Accordingly, systems and methods are needed for accurately measuring, controlling, and automating inventory of product stored in a collapsible tank.